1. Field of the Invention
This invention relates to an electric control of Venetian blind, and of the kind comprising a Venetian blind with head rail, lower list, slats, a drive mechanism with a number of spring clutches for driving a corresponding number of ladder tapes and lift cords and a reversible electric motor for driving a drive shaft of said spring clutches.
2. Discussion of the Related Art
A spring clutch of the above-mentioned kind is known from German Patent Specification No. 1,683,007 and is ordinarily used on Venetian blinds that are operated manually by means of a pull cord. Said spring clutch comprises a drum around which the lift cord of a Venetian blind is wound and which serves to raise or lower said lower list, and a drum around which a specially designed helical spring is wound, the ends of said spring being in engagement with lugs on a ladder tape, said spring being arranged in such a way that by operating the pull cord it is possible to adjust the slats in almost vertical position. By continued pulling action on the pull cord, the lower list may then be raised or lowered.
Since there is a direct mechanical link between the two drums of the spring clutch, the two movements, i.e., the adjustment of the angle and the raising (or lowering), being simultaneously. By proper dimensioning of the diameters of the drums, it is however possible to cause the angle adjustment to occur quicker than the raising or lowering movement itself.
From, e.g., Danish Patent Specification No. 144 894 it is known per se to provide a Venetian Blind with an electric motor for maneuvering said Venetian blind.
By only associating an electric motor with said spring clutches in a control device as defined above one would of course obtain an electrical maneuvering of said Venetian blind, but the two operating steps, i.e. adjustment of the angle of the slats and the raising or lowering are still concomitant, which makes it difficult for the user to effect angular adjustment independently of the raising or lowering.
From U.S. Pat. No. 3,310,099, an electric control of a Venetian blind is known, which comprises essentially an electric unit for manual operation and a mechanism, the particular purpose of which is to ensure parallel guiding of the lower list during its movement up and down and to avoid the lift cords from being paid out in a disorderly fashion when the pulling action due to the lower list weight ceases as some part, such as furniture, interferes with the free movement of the lower list. The mechanism is furthermore so arranged that when the lower list is in its lowermost position, the user is able to perform adjustment of the angle of the slats without concomitant raising of the lower list.
Thus, said prior art device does not give the user the possibility of arbitrary adjustment of the slats by means of said control unit when the lower list is in some position between and uppermost position and a lowermost position. In relation to the above comments on Danish Pat. No. 144 894, it should be emphasized here that said patent specification exclusively deals with the stopping of the Venetian blind in an uppermost or a lowermost position and gives no indication at all regarding an adjustment of the angle of the slats in relation to a raising of lowering of said lower list.